THE HISTORICAL EVOLUTION OF THE MUTUUM CONTRACT: AN ANALYSIS OF THE CLASSICAL SOURCES

Contents: 1. Introduction. 2. The Roman Legal Context and the Formation of Contracts. 3. The Development of the Mutuum contract. 3.1. The Origin of the Obligatio and the Emergence of the Contract. 3.2. Formalism and Contractual Categories in Ancient Rome. 3.3. The Evolution of the Contract over Time. 4. The Development of Real Contracts. 4.1. Constitutive Elements of the Mutuum contract. 4.2. Characteristics of the Mutuum contract. 4.3. Legal Protection of the Mutuum contract. 5. Conclusions. Bibliography.

1. Introduction

The mutuum contract occupies a position of particular significance in the history of obligations law. This relevance derives not only from its practical utility within the everyday economic life of Roman society, but also from its role in the dogmatic consolidation of contractual categories that would later shape the Western legal tradition. Among the various contractual forms recognised in Roman law, mutuum stands out as the paradigmatic example of a real contract, insofar as its formation depended upon the delivery of the thing (datio rei), from which arose the obligation to return an equivalent quantity of the same kind and quality.

The centrality of this institution may be explained on several levels. First, the mutuum contract responded, from an early stage, to a fundamental need within the organisation of social and economic life, allowing individuals to address immediate requirements of subsistence and, later, facilitating the circulation of wealth, financing, and credit. Second, its legal regulation illustrates, with particular clarity, the structural logic of the Roman legal system, grounded in formalism, the typification of obligatory relationships, and the distinction between the different modes through which obligations could arise. Third, the historical development of mutuum reflects, in an exemplary manner, the broader transformation of Roman legal thought, from an approach centred on the objective element of the datio rei and the rigidity of ius strictum, towards a gradual recognition of agreement and the will of the parties.

The present study aims to examine the historical development of the mutuum contract in Roman law, drawing on the classical sources, in order to understand its origin, structure, and evolution. More specifically, it seeks to show that this institution should not be regarded merely as a technical mechanism for the loan of fungible goods, but rather as a legal institution reflecting significant economic, social, and doctrinal transformations.

To that end, the analysis begins by situating mutuum within the broader framework of contract formation in Roman law, examining the relationship between obligatio, contract, formalism, and the various contractual categories. It then turns to the specific development of mutuum, considering its function within Roman economic life and the manner in which its legal contours were progressively shaped by jurisprudence and practice. Finally, attention is given to its constitutive elements, its defining characteristics, and the legal remedies available to the lender.

An examination of the sources supports the view that mutuum, although originally rooted in a primitive framework of trust and solidarity, gradually acquired greater technical and legal refinement as Roman society became increasingly complex. This transformation did not, however, eliminate the institution’s original structure, which remained anchored in the requirement of the delivery of the thing and in the obligation to return the tantundem eiusdem generis et qualitatis. It is precisely this balance between formal tradition and practical adaptation that underlies the dogmatic interest of the Roman mutuum and explains why its study remains essential for understanding the historical foundations of key institutions in contemporary private law.

2. The Roman Legal Context and the Formation of Contracts

As is widely acknowledged, modern Western law has its roots in the Roman legal system. Over time, this system extended far beyond the boundaries of the ancient Roman Empire and came to exert a profound influence on the development of Western legal orders, particularly in the field of civil law.

In fact, since Roman law constitutes the origin of most of the legal institutions that form part of the Western legal tradition, an understanding of Roman legal culture becomes essential for a clearer comprehension of the structure and historical development of contracts.

In this context, it becomes necessary to examine the origins of the mutuum contract through an analysis of its historical development, with the purpose of identifying its distinctive features and the transformations it has undergone since its earliest forms to the present day. Such an approach makes it possible to better understand the sources of current law and the foundations of contemporary legal institutions, particularly in relation to legal relationships that were already central in antiquity, such as the mutuum contract.¹

The mutuum contract can in fact be traced back to very early times, emerging as a practice grounded in reciprocity and, above all, in solidarity. In situations of surplus food production, individuals would provide others with goods exceeding their own needs, later receiving, once circumstances had changed, products of equivalent quantity and quality in return.

This early model can be identified in several ancient civilizations, such as Egypt and ancient Greece, where this type of arrangement was commonly used for the loan of grain. Only at a later stage did loan agreements begin to involve money as their object, a development that can be observed, for example, in Egypt.²

A particularly significant presence of mutuum-type arrangements can be observed in maritime transactions, later referred to as maritime loans, in which the lender’s profit was directly linked to the success of the venture. Under this arrangement, if the enterprise proved successful, the lender would obtain the expected return, if it failed, the lender bore the risk of loss.³

In Roman society, particularly during the monarchical period and the early Republic, the mutuum contract developed more gradually. Given the predominantly agrarian character of Roman society at that time, no clear distinction initially existed between different forms of loans.

Such agreements were initially concluded within the family circle and only later extended to neighbours. These contractual relationships were founded primarily on the trust established between the parties, as they typically concerned loans of consumable goods and were concluded without remuneration. In other words, the lender did not derive any profit from the transaction, which allows these arrangements, in many cases, to be understood essentially as acts of giving.^4,5

For a considerable part of Roman history, loans for use, safekeeping, and consumption, generally concerning basic goods, were not clearly distinguished from one another. Only toward the end of the Republic, or at the beginning of the Principate, did mutuum emerge as a distinct legal institution within the praetorian notion of credere. At that stage, the praetor introduced actiones in factum in order to provide legal protection for arrangements such as commodatum and pignus.⁶

Despite the slow process through which mutuum was consolidated as a legal institution in ancient Rome, it ultimately came to assume a structure largely consistent with that which would later be adopted, over time, in various legal systems.

In this respect, the Portuguese legal system is no exception. In its current formulation, the mutuum contract is legally defined in Article 1142 of the Portuguese Civil Code (CC) as: “o contrato pelo qual uma das partes empresta à outra dinheiro ou outra coisa fungível, ficando a segunda obrigada a restituir outro tanto do mesmo género e qualidade.”^7,8,9

If one considers the wording of the law, it becomes clear that the essential structure of the mutuum contract remains, to a large extent, faithful to the model outlined in Roman law. In that context, mutuum consisted in the transfer of ownership of fungible goods from the lender to the borrower, who thereby assumed the obligation to return the tantundem eiusdem generis et qualitatis, that is, an equivalent amount of the same kind and quality. It was precisely around this model of datio that Roman jurisprudence consolidated the notion of the real contract, giving rise to sustained doctrinal interest over the centuries.¹⁰

In these terms, and from an etymological perspective, it remains appropriate, following the words of Gaius, to describe this contract as it is called, mutuum because what is thus given to you by me becomes, from mine (meum), yours (tuum). In turn, mutuum is related to the root mov, from which movere and mutare derive, conveying the idea of exchange or change of place. In mutuum, accordingly, one observes the exchange of fungible things for others that are likewise fungible.¹¹

3. The Development of the Mutuum contract

3.1. The Origin of the Obligatio and the Emergence of the Contract

In light of the foregoing, it becomes necessary to examine the historical development of the contractual figure over time. Particular attention must be given to the fact that, although the mutuum contract forms part of obligations law, this does not mean that its existence coincided with, or preceded, the emergence of the concept of obligation. In fact, the notion of obligatio, predates the abstract elaboration of the concept of contract.¹²

In the Institutes of the Justinianic period, obligatio was defined as a legal bond by which we are necessarily bound to render something in accordance with the law of our city.^13,14

By contrast, the concept of contractus appears in Roman law through the writings of the jurists already in the classical period, as a way of expressing what had been concluded through formulations such as res contracta (a contracted matter or the object of a contract), contrahenda (that which is to be contracted), and negotium actum or contractum (a transaction concluded or a contract entered into), used to describe legal transactions that gave rise to obligations.¹⁵

This understanding is also confirmed by the way in which mutuum was treated in the classical sources. As can be seen in the work of Gaius, mutuum was regarded as a paradigmatic instance of an obligation arising from the delivery of a determinate thing, forming part of the system of restitutionary actions based on typical grounds for recovery. It does not, therefore, appear as a contract endowed with an autonomous legal regime, but rather as the cause justifying restitution. The absence of a separate title devoted specifically to mutuum in the Digest, unlike what occurs with other contractual figures, reinforces this interpretation, since issues relating to mutuum were addressed mainly within the framework of the condictio certae rei (the action for the recovery of a specific thing). This approach suggests that the practice of mutuum preceded the systematic formulation of the contract as a technical legal category, and that its relevance lay primarily in its concrete function as a transfer of ownership accompanied by an obligation of restitution.¹⁶

In this sense, in Roman law the contract was not merely an agreement of wills, but rather a legally recognised instrument that, in accordance with the schemes characteristic of classical law, gave rise to an obligatory relationship.¹⁷

This interpretation is particularly evident in the case of mutuum, whose central place within the legal system is reflected in its prominent treatment in the Institutiones of Gaius and of Justinian. In these didactic works, mutuum appears as a distinct legal figure, even though, as noted above, classical legal doctrine did not grant it a fully autonomous systematic treatment in the Digest.¹⁸

3.2. Formalism and Contractual Categories in Ancient Rome

In the archaic period, a mere agreement of wills was insufficient for the formation of a contract. Roman law adopted a far more restrictive conception of contracts than that found in modern legal systems, recognising as contracts only those agreements intended to create obligations and which also satisfied an objective requirement. This requirement consisted in compliance with the ritual formalities necessary for the contractual act, since only through the observance of such formalities could obligations effectively arise.

The jurists of the classical period, rather than conceiving contracts as a general and unified category, instead recognised certain specific contractual types endowed with autonomous legal regimes, in which the corresponding obligation arose not from the subjective element (pactum, conventio), but as a consequence of an objective element, expressed in the observance of formalities or in the delivery of the thing (forma, datio rei).¹⁹

Roman law was profoundly formalistic, requiring the observance of rituals and rigid procedural schemes for the validity of contracts. As a result, contracts acquired legal effectiveness only if they complied with specific forms, such as those concluded verbis, litteris, or re. Formalism thus constituted an essential feature of the system, ensuring legal protection for creditors.²⁰

Thus, given the objective character of Roman law, little inclined toward abstraction and largely focused on concrete situations, formal requirements, and ritualised acts, contracts could not be recognised unless they were expressed through a form, falling within one of the following three categories:

a) verbis, which had both a religious and a practical function, and required the formulation of strict oral declarations, according to a predetermined wording;

b) litteris, which consisted in obligations created through a written entry in the creditor’s accounts, such as the transcriptio, whereby the debt was recorded in the creditor’s ledger; and

c) re, in which the essential element for the formation of the contract was the delivery (traditio) of the thing.²¹

This requirement of the effective delivery of the thing, as a constitutive element of the obligation reflects a deeply objective conception of the contractual bond. In this framework, traditio, or datio rei, was not merely a moment of performance, but rather the fundamental legal act from which the obligatio arose. The delivery of the thing functioned as a clear and observable criterion for the existence of the legal bond, reflecting a concern for legal certainty and evidentiary reliability in judicial proceedings, within a system in which the will, abstractedly considered, had not yet acquired sufficient autonomous value to produce binding legal effects.²²

The contract was not confined to mere consensus, since an obligation arose only when the legal order recognised the relationship as a valid juridical source, requiring the observance of formalities in order to ensure the effectiveness of obligatory bonds.²³

Accordingly, contracts did not arise from the mere expression of the parties’ will, but from compliance with solemn forms and strict requirements, the observance of which was essential for the creation of legally recognised obligations.²⁴

The contract was, therefore, a formally recognised legal act that produced obligatory effects, only when concluded in accordance with the forms prescribed by the legal order.²⁵

For the obligatio to arise, an additional element beyond the mere agreement of wills was required. This element emerged when the agreement (consensus) became associated with solemn acts such as the stipulatio and the nexum.²⁶

The stipulatio was a formal verbal contract consisting in the pronouncement of solemn words, formulated according to a predetermined sequence of question and answer, the completion of which brought the contract into existence. The formalism required for its conclusion was regarded as essential, as it made clear to the parties that the creditor’s expectations were legally protected, through the explicit articulation of a serious consequence for the debtor in the event of non-performance of the agreement.²⁷

It constituted one of the principal contractual models of ancient Rome, distinguished by its formal and verbal character. This type of contract required a specific exchange of solemn words between the parties and functioned as a flexible legal instrument capable of serving various purposes, including guarantees, sales, and promises of payment.²⁸

For its part, the nexum was a contract concluded per aes et libram, that is, a formal act performed before witnesses with the use of copper and scales. Under this arrangement, the debtor, or a member of the debtor’s family, became subject to the creditor’s power in the event of non-performance. The nexum may be understood as a form of loan endowed with executory force, since it allowed the creditor, in case of default, to reduce the debtor or the debtor’s relative to a condition of servitude.²⁹

This contract operated as a form of security for a loan, and until the debt was discharged, or until the solutio per aes et libram, corresponding to the formal act of releasing the debt, took place, the debtor remained in a condition comparable to that of a slave. During this period, the creditor could keep the debtor in chains or compel him to work, benefiting from his labour until the obligation was satisfied.³⁰

Another relevant example of a formal legal act concluded per aes et libram was the mancipatio, an early form of the contract of sale. Although it shared with the nexum the same ceremonial formalism and the solemn words pronounced before witnesses, its purpose was the transfer of ownership. It was a transaction that required the purchaser to recite specific solemn formulas, and to make a symbolic payment with a piece of bronze, which, when struck against one of the scales, represented the weighing corresponding to the price to be paid.³¹

3.3. The Evolution of the Contract over Time

Subsequently, during the time of Gaius, a further contractual category was added to those previously identified, verbis, litteris, and re, that was based on consensus. As a result, four types of contracts came to be recognised, each requiring compliance with specific formalities that were legally defined and typified. These formalities were to be interpreted strictly, since the obligation arose from the objective element of the contract, while the will of the parties was still not regarded, at that stage, as an independent source of the obligation.³²

“Et prius videamus de his, quae ex contractu nascuntur. Harum autem quattuor genera sunt: aut enim re contrahitur obligatio aut verbis aut litteris aut consensu.”³³

Thus, up to that period, the prevailing view was that the obligation was constituted on the basis of the objective element of the transaction. Only in the Justinianic era did a conceptual shift occur that allowed, at least partially, the unification of the notions of contract and agreement. In this context, the Justinianic compilation brought about a reformulation of the concept of contract, and conventio came to be regarded as the essence of the obligatory relationship, allowing consensus to assume a central role as the criterion for contractual validity.^34,35

Byzantine jurists departed from the earlier classical view that obligations arose from an objective element, and moved away from the traditional contractual categories, re, verbis, litteris, and consensu, placing primary importance on the will of the parties. The prevailing understanding became that an obligation no longer resulted from the objective element itself, but from the agreement of wills between the parties, which constituted the common basis of the various obligations. These would then be completed through a specific material act, whether by the delivery or transfer of the thing, or by the observance of the formalities required for their validity.³⁶

In fact, this transition from the objective element to the primacy of consensus did not occur abruptly, but rather resulted from a gradual doctrinal and practical evolution. As legal scholarship has emphasised, the shift from the formal rigidity of the classical categories to a more flexible system grounded in the agreement of the parties must be understood in light of the social, economic, and cultural transformations that marked the end of the Republic and, above all, the post-classical period. The original formalism of mutuum as a re contract, founded upon the delivery of the thing, was progressively reconfigured, not only with regard to its economic function but also in its legal framework. This development reflects a broader transformation in the Roman law of contracts.³⁷

This development, particularly evident in the post-classical and Byzantine periods, reflects a departure from the earlier objectivist structure, as consensus gradually came to assume primacy in the formation of obligatory bonds. The agreement of wills thus became, even when still subject to certain formal requirements, the true generating element of the obligatio, including in contracts that had traditionally been classified as real contracts.

Although, in the case of mutuum, even after consensus had been reached, the obligation arose only upon the effective delivery of the thing, the so-called datio mutui, which transferred ownership of a fungible good and generated the obligation to return an equivalent in kind and quality. The figure of mutuum thereby emerged as the archetype of the real contracts, requiring for its completion both consensus and a material act of performance, without which no obligatory bond came into existence.

The criterion of full consensuality only emerged at a later stage, and even then, reservations remained regarding its application to real contracts. The legal regime governing loans reflected this initial rigidity, in which the mere agreement of wills was insufficient to create an autonomous obligatory bond. As illustrated by the rules concerning the stipulation of interest (foenus), the validity of the agreement often depended on compliance with prescribed forms, revealing the persistence of contractual formalism. Moreover, the regulation of interest rates and the sanctions associated with non- performance, demonstrates a growing concern for balance within obligatory relationships, thereby reinforcing the social function of mutuum within the Roman legal order.^38,39

In practice, the Roman contractual system underwent a gradual process of opening, in which conventio increasingly gained prominence as an expression of private autonomy, even where the contract still required a material element for its completion. This development led to a growing recognition of the obligatory bond as a projection of the common will of the parties, allowing contractual relations to expand beyond the rigid frameworks of the classical tradition.

4. The Development of Real Contracts

Among the contracts that were not considered perfected on the basis of consensus alone, requiring instead an additional material act for their constitution, were the so-called real contracts. In Roman law, this category included the mutuum contract, the contract of commodatum, the contract of pignus, and the contract of depositum.

However, these contracts did not share the same legal nature. In fact, the contracts of commodatum, pignus, and depositum were regarded as bonae fidei contracts, meaning that, in the event of litigation, the judge was entitled to assess the transaction between the parties in accordance with equity and good faith in the performance of the obligations. By contrast, mutuum was classified as a contract of ius strictum.⁴⁰

In fact, among the real contracts, mutuum early distinguished itself by its practical relevance and its close connection with Roman economic and social life, which justifies a more detailed examination of its historical development. Although the precise historical moment of the emergence of the mutuum contract is unknown, it is generally accepted that it is a legal institution of very remote origin. Its presence was already essential and deeply rooted in archaic Rome, responding, as noted earlier, to a basic need for subsistence and being frequently used to address temporary shortages within agricultural and pastoral contexts.

In a society lacking a structured financial system, marked by scarcity of resources and dependence on natural cycles, mutuum functioned as an instrument of solidarity, grounded in values such as fides (good faith), trust, and friendship. The loan for consumption, informal and devoid of formal guarantees, rested on the moral expectation that what had been received would be returned in an equivalent quantity and quality.⁴¹

In reality, although the mutuum contract originally emerged as an act of solidarity between individuals bound by close and trust- based relationships, intended to address temporary needs without any expectation of remuneration, it gradually evolved as these relationships expanded.⁴²

With Rome’s expansion across the Mediterranean, particularly from the third century BC onward, together with its gradual opening to international trade and the influx of wealth, mutuum underwent a process of functional transformation and began to play a role in the financing of economic activities. Urban growth, the expansion of commercial exchange, and the emergence of a new mercantile and financial class, made the use of mutuum increasingly common as a means of access to credit for entrepreneurs and traders. The figure of the simple lender gave way to that of the professional banker, who not only lent his own capital, but also received deposits and carried out more complex financial operations.⁴³

This new economic context, grounded in the growing importance of banking activity and monetary circulation, led to the increasingly frequent use of mutuum with interest. This development required the legislator to impose normative limits on interest rates and to establish consequences for cases of usury. Although interest- bearing loans were not prohibited, the perception of disproportion between the amount lent and the repayment demanded in certain situations prompted regulatory restrictions in the name of the public interest and the protection of debtors, anticipating concerns that would later assume a central place in modern legislation on credit.⁴⁴

In fact, the mutuum contract did not remain confined to its original function. From this initial informal model based on trust, it gradually underwent transformations until it became a typified contract, protected by the legal order and consolidated as a unilateral contract of ius strictum, subject to legal mechanisms ensuring its enforcement.⁴⁵

The increasing sophistication of the Roman economy gave rise to a functional duality in the use of mutuum, which came to operate both as an instrument of consumption and as a means of investment. Alongside the traditional mutuum pauperum, typical of the economically weaker strata and intended to meet immediate needs, a new form of mutuum emerged, directed toward the financing of commercial and entrepreneurial activities. This development was closely connected with the growth of banking activities, marked by the appearance of argentarii and coactores argentarii, professionals who intermediated credit operations and advanced sums for acquisitions at public and private auctions. These agents, comparable in some respects to modern banks, operated with instruments such as bills of exchange, systems of guarantee, and increasingly sophisticated accounting techniques. This evolution shows that, even while retaining its structure as a real contract based on the datio rei, mutuum became compatible with a wide range of financial transactions, responding to the expanding demands of Roman economic life.⁴⁶

Its regulation ultimately led to the creation of specific actions by the praetor to ensure the restitution of the thing lent, among which the condictio was particularly significant. This procedural remedy allowed the lender to demand from the borrower the return of the loaned property, on the basis that the defendant held a thing which, under the law, he was bound to restore to the claimant. Accordingly, the condictio must be understood within the framework of contracts of ius strictum, where the judicial decision was confined to the application of the formally established rule, without recourse, unlike in other real contracts, to considerations of equity.^47,48

As mutuum became increasingly frequent in commercial and financial transactions, a growing tension emerged between the rigidity of its structure as a real contract, dependent on the datio rei, and the new practical demands of commerce, which required more rapid and effective solutions. Roman law never formally recognised a consensual mutuum, yet the sources reveal a gradual enhancement of the role of the parties’ will, particularly through the use of legal devices such as the stipulatio, which made it possible to reinforce the obligatory bond even before the delivery of the thing. Thus, although the traditional model based on the datio mutui continued to prevail, a clear doctrinal tendency developed toward overcoming the limitations imposed by realitas, paving the way for more flexible legal formulations, better suited to the expanding financial practice. This tension between formal structure and the autonomy of the parties’ will, therefore, characterises the final stage in the development of mutuum within the Roman legal system, while, at the same time, foreshadowing later doctrinal debates concerning the concept of contract.⁴⁹

At this final stage in the development of the Roman mutuum, one can observe a tension between the traditional formalism centred on the requirement of datio rei and the gradual acceptance of more flexible contractual mechanisms grounded in the autonomy of the parties’ will. In this context, stipulatio came to play a significant role as a means of reinforcing obligations arising from prior agreements, making it possible to anticipate obligatory effects even before the delivery of the thing.

As can be observed in the later legal experience of the Roman Empire, mutuum remained a central institution in the granting of credit, but gradually became more permeable to flexible practices and interpretations, particularly in a context of increasing commercial complexity. This coexistence between formal structure and the will of the parties reveals the hybrid character of Roman mutuum, as an institution situated between the model of ius strictum and the principles of modern contractual consensualism, thereby anticipating foundations that would later be consolidated within the Western legal tradition.⁵⁰

4.1. Constitutive Elements of the Mutuum Contract

As noted above, the mutuum contract was a unilateral contract through which one party received ownership of a certain pecunia or of another fungible thing, thereby assuming the obligation to return an equal quantity of the same kind and quality. It may therefore be considered that the contract was constituted by three fundamental elements: the conventio, the datio rei, and the object.⁵¹

The conventio consisted in the agreement by which the borrower undertook the obligation to return an equivalent amount of pecunia received or goods of the same nature and quality as the res that had been lent. Accordingly, it was essential that the agreement established the borrower’s duty to restore an equal quantity of money or goods of the same kind and quality as those that had been the object of the loan.

Legal scholarship has recognised that, although mutuum was originally based on the delivery of the thing, the agreement of wills soon came to assume a decisive role, influencing the very scope of the obligation arising from the datio and allowing the parties to determine elements such as the place and time of restitution.⁵²

In fact, the increasing relevance of conventio as an autonomous normative element within mutuum is also attested by the Roman sources, which show how the mere agreement between the parties could determine not only ancillary aspects but also decisive elements of the obligatory bond, such as the locus solutionis, even where this did not result from a formal stipulation.⁵³

For its part, an understanding of datio rei requires a prior analysis of the general structure of mutuum as a real contract, whose completion depended upon the delivery of the thing lent. In the Roman legal context, mutuum was regarded as a real contract whose perfection required the delivery (datio) of the object. From that moment, ownership of the fungible goods was transferred to the borrower, giving rise to the obligation to return an equivalent in kind and quality.

This structure implied that the lender had to be the owner of the thing lent and possess the legal capacity to transfer it. Roman jurisprudence addressed this reality under the designation datio mutui, an expression that emphasised the material character of delivery as the constitutive condition of the obligatory relationship. The borrower became the owner of the thing lent, assumed the risk of its loss (periculum), and was free to dispose of it, provided that restitution was ensured, generally within the agreed period. Restitution could be claimed through the action condictio, which was based on the equivalence between the thing delivered and that which had to be returned, reflecting the logic characteristic of unilateral contracts and of ius strictum.

This essential requirement of the transfer of ownership through delivery distinguished mutuum from depositum. Although both were real and gratuitous contracts, mutuum differed from depositum not only because it was a unilateral contract, but above all because its fundamental legal effect consisted in the transfer of ownership between the parties.⁵⁴

This distinction could, however, become blurred when the deposit concerned fungible goods, since, if the depositary was permitted to use the thing, the relationship would in fact correspond to a mutuum rather than to a true deposit:

“Deposui apud te decem, postea permisi tibi uti: Nerva Proculus etiam antequam moveantur, condicere quasi mutua tibi haec posse aiunt, et est verum, ut et Marcello videtur: animo enim coepit possidere. Ergo transit periculum ad eum, qui mutuam rogavit et poterit ei condici.”⁵⁵

In fact, this fragment shows that, once the depositary was authorised to use the fungible goods delivered, even if they had not been physically moved, the jurists Nerva, Proculus, and Marcellus considered that the situation should be treated as a mutuum. This was because the depositary came to possess the goods animo domini, that is, with the intention of acting as their owner. Such a change in the nature of possession therefore entailed the transfer of the risk (periculum) and made it possible to demand restitution through the action condictio, thereby confirming the transformation of the deposit into a mutuum from a legal standpoint.

Thus, for example, the figure known as depositum irregularis was, in reality, a disguised mutuum, since the delivery accompanied by animus transferendi dominii and the fungible nature of the thing entailed the transfer of ownership and the replacement of the duty of custody with an obligation to restore an equivalent.⁵⁶

In Roman banking practice, the depositum irregularis was common in dealings with the argentarii, where the depositary was allowed to dispose of the deposited property, undertaking only to return an equivalent amount. This practice effectively produced an assimilation between deposit and mutuum, revealing the permeability between juridical categories that were formally distinct but functionally convergent.

This distinction between mutuum and depositum, centred on the transfer of ownership effected through the datio rei, prepares the ground for the analysis of the third essential element of mutuum: the res.

In fact, the nature of the object lent played a decisive role in the legal configuration of the contract. Historiography has shown that, in the early Roman conception, it was precisely the res, as the object of delivery, that possessed sufficient obligatory value to justify, in itself, the emergence of the obligation. This understanding was consistent with the logic underlying other obligatory situations arising from the delivery of a thing, such as the payment of what was not owed (solutio indebiti) or the datio ob causam.⁵⁷

Finally, the object of the loan, the thing lent, had to be fungible in nature, since the essence of the transaction laid in the borrower’s obligation to return to the lender a thing identical in kind to that which had been lent. Consequently, if the object delivered were non- fungible, restitution in those terms would be impossible, and the relationship could not be classified as a mutuum contract.⁵⁸

The requirement of fungibility did not, however, prevent certain goods, though not traditionally fungible, from being treated as such by the parties where there was an intention to restore an equivalent rather than the very same thing. This conceptual flexibility allowed mutuum to be adapted to a wider range of practical situations, bringing it closer to other legal figures such as datio ob causam and condictio, with which it shared the logic of restitution by equivalence. Roman jurisprudence, in addressing these related institutions, confirmed that the transfer of ownership accompanied by an obligation of equivalent restitution could also occur outside the strict framework of mutuum, demonstrating how the model of mutuum broadly influenced the development of obligations arising from the delivery of a thing.⁵⁹

4.2. Characteristics of the Mutuum Contract

Although, in its origins, the mutuum contract was essentially gratuitous, the charging of interest was gradually admitted, albeit always subject to an additional degree of formalism. In classical Roman law, interest (usura) did not arise automatically from the nature of the loan; rather, it required an express supplementary agreement, generally concluded through an autonomous stipulatio, distinct from the mere datio rei. Usura was thus understood either as the price for the use of money (usus aeris) or as compensation for the risk borne by the lender (sortis periculum), as reflected in fragments attributed to Paulus and Papinian. Only with the development of the Justinianic system did the charging of interest come to be recognised more broadly in law, even in the absence of a prior written agreement.

In its primitive form, mutuum was essentially gratuitous, a characteristic that resulted not only from technical or procedural considerations but also from ethical foundations deeply rooted in Roman legal thought. This gratuitous nature reflected a clear moral stance, as profit derived from lending was viewed with suspicion by jurists and legislators. This attitude is evidenced by the severe penalties established in the Twelve Tables against the feneratores, whose activity was equated with that of manifest thieves and punished with particularly harsh sanctions. The early system of remedies for non-performance, relied on strict actions, such as the actio sacramenti and, later, the condictio, both aimed at securing the simple restitution of what had been delivered.⁶⁰

This aversion to unjustified profit was also reflected in strict measures such as the senatusconsultum Macedonianum, which prohibited the judicial enforcement of debts contracted by filii familias, precisely in order to prevent abuses by creditors. Roman legislation thus sought to distinguish between legitimate loans and usurious practices, tolerating foenus only when previously stipulated, at defined rates and within certain legal limits.⁶¹

Moreover, the mutuum contract displayed a clearly unilateral structure, as it originated from a legal relationship that was itself strictly unilateral, in which the only obligation rested with the borrower, consisting in the duty to return to the lender a thing of the same kind and quantity.

This configuration reinforced the gratuitous character of the contract, implying that the value of the thing delivered by the lender determined the maximum amount to be restored, although nothing prevented the restitution of a lesser amount. Only the upper limit of the prestation was fixed by the value of the thing lent, since the absence of an agreement on interest excluded any increase in the amount to be returned.⁶²

The distinction between the various ways in which obligations could arise in Roman law was already the subject of reflection in the classical period, as evidenced by Ulpian when citing Labeo in the context of the edictum praetoris urbani. According to this doctrine, certain situations are regarded as “done” (agantur), others as “carried out” (gerantur), and others as “contracted” (contrahantur). The term actum thus designates, in a general sense, any act capable of producing legal effects, whether verbal or real, as occurs in the stipulatio or in the numeratio. By contrast, contractum refers to a bilateral obligation arising from an agreement of wills, as in sale, lease, or partnership. The term gestum, in turn, denotes an act performed without verbal formalisation, as occurs in certain real contracts. This tripartite distinction helps to clarify the unilateral structure of mutuum, which, not being a bilateral contractum but rather a contract of ius strictum, was closer in nature to gestum, even though it was formalised through the datio rei and could be reinforced by verbal mechanisms such as the stipulatio.⁶³

Despite this, the principle of gratuitousness admitted several exceptions. Notable among these were loans of goods, loans granted by cities, loans provided by banks, and maritime loans to shipowners or merchants (foenus nauticum). In fact, within the Roman society, the activity of granting loans with interest developed considerably and came to be clearly regulated by law.⁶⁴

This activity, however, was not free from controversy. The excessive charging of interest, the so-called foenus excessivum, was subject to significant legal restrictions, particularly concerning the maximum permissible rate (usurae legitimae), the requirement of written stipulation, and the possible nullity of the loan where such limits were exceeded. The repression of excessive profit was grounded in an ethical conception of mutuum as an instrument of assistance rather than exploitation. This approach was also reflected in the regulation of foenus nauticum, which was permitted only in specific contexts, such as the financing of maritime ventures, where the high level of risk justified the additional premium.

Roman jurisprudence expressly recognised the validity of mutuum with interest, provided that the interest was properly stipulated and did not exceed the authorised rates. Such stipulations could take the form of ancillary clauses attached to the principal contract or be formalised through a stipulatio usurarum, a separate verbal contract that fixed the amount and duration of the interest. This solution made it possible to reconcile the unilateral and originally gratuitous structure of the traditional mutuum with the practical need to remunerate credit in economic activities, particularly through the foenus nauticum, in which the creditor assumed the risk associated with the maritime voyage.⁶⁵

Moreover, Roman mutuum was, above all, a real contract, whose completion depended on the effective delivery of the thing, without which no obligation of restitution arose. This structural characteristic was reflected, for example, in the requirement of numeratio, that is, the actual delivery of the sum lent to the debtor, in the absence of which no enforceable legal bond came into existence.⁶⁶

The requirement of numeratio was so central that, in the absence of proof of delivery, the existence of a mutuum was not admitted, even where a prior agreement between the parties could be established. This rigidity shows that, within the Roman model, the material completion of the contract preceded any legal effect, thereby excluding the possibility of a purely consensual mutuum.⁶⁷

Nevertheless, the conditions required for the validity of mutuum were the following: a) The object of the loan had to consist of things capable of being weighed, counted, or measured, such as wine, grain, oil, among others; b) The things delivered to the borrower had to be transferred with the title of ownership (mutui datio). The transfer of ownership was effected through traditio; c) There had to be an agreement of wills between the parties concerning the loan, an agreement between creditor and debtor whereby the debtor undertook to repay what had been received within the agreed period, in the same quantity and quality. This agreement did not allow the borrower to return more than had been received, since the obligation arose from the delivery of the thing itself.

4.3. Legal Protection of the Mutuum Contract

In the event of non-performance by the borrower, the lender, although not protected by a specific action created exclusively for mutuum, could rely on one of two actions to assert his right: the actio certae creditae pecuniae or the condictio triticaria (or condictio certae rei).⁶⁸

Where the object of the mutuum consisted of a sum of money, the lender could bring the actio certae creditae pecuniae, an action aimed at recovering a specific amount of money owed to the creditor. By contrast, the condictio triticaria (or condictio certae rei) was the action used to recover an equivalent quantity and quality of fungible goods previously delivered by the lender to the borrower, where the object of the loan consisted of fungible things other than money.^69,70

The actio certae creditae pecuniae and the condictio triticaria were both typical actions of the formalistic Roman system of justice, structured according to rigid procedural models and suited to the protection of purely patrimonial interests. These actions, grounded in the restitution of fungible goods, were limited to the proof of the datio and of the precise amount of the obligation to restore, leaving no room for equitable or discretionary assessment by the judge.

They followed the logic of contracts of ius strictum, being confined to the application of formally established rules, without regard to considerations of equity, unlike what occurred in contracts of bonae fidei. This procedural rigidity in the treatment of mutuum within Roman law was consistent with its character as a unilateral and formal contract, whose legal protection rested exclusively on the verification of the delivery (datio rei) and of the corresponding obligation.^71,72

This same rigidity is confirmed by the legal sources themselves, particularly in D.12.1.11, §1, where Ulpian, citing Proculus, states that if ten coins are delivered to the borrower under an agreement that only nine are owed, the borrower cannot be compelled, as a matter of strict law, to pay more than nine. Conversely, if it is stipulated that, for ten received, eleven are to be repaid, the lender may not claim more than the amount actually delivered:

“Si tibi dedero decem sic, ut novem debeas, Proculus ait, et recte, non amplius te ipso iure debere quam novem. Sed si dedero, ut undecim debeas, putat Proculus amplius quam decem condici non posse”.⁷³

In other hand, in D.45.1.68, the view is reinforced that, even where a prior agreement exists, the effects of the promise are strictly delimited, and protection may extend only to obligations that are certain and precisely determined:

“Si poenam stipulatus fuero, si mihi pecuniam non credidisses, certa est et utilis stipulatio. Quod si ita stipulatus fuero: "pecuniam te mihi crediturum spondes?", incerta est stipulatio, quia id venit in stipulationem, quod mea interest.”⁷⁴

These texts illustrate the rigorous application of ius strictum to the mutuum contract, focusing the protection of the lender on the effective delivery of the thing and on the exact identity of the obligation undertaken.⁷⁵

However, despite the rigidity of the protection afforded by the actions available to the lender, namely the actio certae creditae pecuniae and the condictio triticaria, Roman commercial practice occasionally sought to circumvent the strict requirements of the real contract through the use of the stipulatio. The formal promise to grant a mutuum, although initially viewed with reservation by the legal tradition, was known and admitted in classical Roman law, particularly when accompanied by a penal clause.

As the jurist Paulus observed in D.45.1.68, where a penalty was stipulated for the non-performance of a promise to grant a mutuum, such a stipulation could give rise to a definite and enforceable obligation, otherwise, only the actual loss suffered by the promisee, id quod interest, could be recovered.⁷⁶

The stipulatio thus emerged as a useful instrument for anticipating the obligatory effects of mutuum, enabling the creditor to secure the performance of the agreement even before the effective delivery of the thing. Although characterised by its verbal formalism, this device helped to mitigate the rigidity of mutuum as a real contract, bringing it closer to more flexible forms of contractual arrangement.

This flexibility introduced through the stipulatio, although exceptional, reveals an attempt by the Roman system to adapt to the demands of commercial practice, particularly in situations where the delivery of the thing had not yet taken place. In the context of mutuum, this development reflects a certain openness of the Roman legal system to forms less dependent on the materiality of the datio and more oriented toward consensuality.

5. Conclusion

The analysis undertaken allows the conclusion that the mutuum contract represents one of the most significant institutions of Roman law within the field of obligations, not only because of the frequency of its practical use, but above all, due to the doctrinal importance it assumed in the historical formation of Western contractual thought. Mutuum illustrates particularly clearly the logic of the Roman legal system, characterised by a typified structure of the sources of obligations, by strong formalism, and by the central role of the datio rei as the constitutive element of the obligatory bond.

It was observed that the origin of mutuum precedes its conceptual autonomy as a contract. Before emerging as a technically defined legal institution, mutuum existed as a social practice of assistance, grounded in trust and reciprocity, particularly within agricultural contexts and situations of scarcity. Only gradually, and in connection with the economic and commercial development of Rome, was this practice absorbed into the legal order, becoming integrated within the category of real contracts and benefiting from its own procedural protection.

From a structural perspective, mutuum established itself as a unilateral, real contract of ius strictum. Its completion depended on the delivery of a fungible thing and the transfer of the corresponding ownership to the borrower, from which arose the obligation to return an equivalent in kind and quality. This configuration shows that, in the classical Roman model, the mere agreement of wills was insufficient to generate the obligatory bond, clearly distinguishing mutuum from modern conceptions based on the predominance of consensus. Nevertheless, the evolution of the sources reveals a growing recognition of the importance of conventio, as well as the use of complementary instruments, such as stipulatio, capable of reinforcing or anticipating obligatory effects.

The functional transformation of mutuum constitutes another central aspect of its development. From a primitive instrument of solidarity and subsistence, mutuum came to play a significant role in financing economic activity, accompanying the commercial, urban, and banking expansion of Rome. This change contributed to its increasing legal sophistication and to the emergence of new tensions between the rigidity of the contract’s formal structure and the practical demands of an expanding economy. The regulation of interest, the limitations imposed on foenus, and the normative intervention against usury further demonstrate that mutuum also lay at the centre of ethical, social, and political concerns.

From a procedural standpoint, the legal protection afforded to mutuum confirms its classification within the framework of ius strictum. The actio certae creditae pecuniae and the condictio triticaria reflected a form of protection based on proof of delivery and on the precise determination of the prestation owed, leaving little room for considerations of equity. This regime reveals an internal coherence between the nature of the contract and the legal mechanisms available for its enforcement, reinforcing the idea that mutuum was conceived in Roman law as a strictly defined institution, albeit one capable of functional adaptation.

In summary, the study of Roman mutuum shows that this institution played a decisive role in the formation of the dogmatics of obligations, constituting a fundamental link between archaic economic practices and the construction of legal categories that continue to structure private law today. Its development reveals not only the capacity of Roman law to respond to the concrete needs of social and economic life, but also the depth of its influence on the European legal tradition. The mutuum contract should therefore be understood as a historically dynamic, legally sophisticated institution that is doctrinally central to the understanding of obligations law.

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